/Engine/Source/Runtime/Engine/Classes/Engine/World.h
Asynchronously loads the given levels in preparation for a streaming map transition. This codepath is designed for worlds that heavily use level streaming and GameModes where the game state should be preserved through a transition.
void PrepareMapChange ( const [TArray](API\Runtime\Core\Containers\TArray)< [FName](API\Runtime\Core\UObject\FName) > & LevelNames )